The present invention relates to a valve timing control system for an internal combustion engine, which performs variable control of opening and closing timing of an intake or exhaust engine valve in accordance with the engine operating conditions.
Typically, the valve timing control system controls opening and closing timing of an engine valve by controlling the phase of rotation of a crankshaft and a camshaft on a power transfer path from the crankshaft to the camshaft. Specifically, the system comprises a driving rotator coupled to the crankshaft through a timing chain and the like, a follower rotator coupled to the camshaft and to which the driving rotator is mounted to enable relative rotation as required, and a mounting-angle control mechanism interposed between the two rotators to control a mounting angle formed therebetween. Operating-force providing means provide an operating force to the mounting-angle control mechanism when required to change the phase of rotation of the crankshaft and the camshaft.
Various types of mounting-angle control mechanisms have been developed, one of which uses a helical gear to convert rectilinear operation of a hydraulic piston to rotary operation of the driving and follower rotators. Recently, a mounting-angle control mechanism using a link is proposed which has many advantages such as shortened axial length and less friction loss.
However, as will be described hereinafter, with the valve timing control system including a link as mounting-angle control mechanism, when the system undergoes great torque variation, for example, an engaging part of a guide member or movable guide can be disengaged from a spiral guide, disturbing smooth operation of the guide member.
It is, therefore, an object of the present invention to provide a valve timing control system for an internal combustion engine, which contributes to smooth and accurate operation of the guide member along the spiral guide at all times.
The present invention provides generally a system for controlling a valve timing in an internal combustion engine, which comprises: a driving rotator rotated by a crankshaft of the engine; a follower rotator provided to a camshaft of the engine, the follower rotator receiving power from the driving rotator; a radial guide provided to one of the driving rotator and the follower rotator; an intermediate rotator arranged rotatable with respect to the driving rotator and the follower rotator, the intermediate rotator comprising a spiral guide in a face opposite to the radial guide; a movable guide movably engaged with the radial guide and the spiral guide; a link which swingably couples another of the driving rotator and the follower rotator at a position distant from a center of rotation thereof to the movable guide; and a device which provides to the intermediate rotator an operating force for rotation with respect to the driving rotator and the follower rotator, the device making radial displacement of the movable guide engaged with the spiral guide along the radial guide, the radial displacement being converted into relative rotation of the driving rotator and the follower rotator through the link, wherein the movable guide comprises a main body supported by a front end of the link, an engaging part movably provided to the main body and engaged with the spiral guide, a biasing device which biases the engaging part to the spiral guide, and a restraining device which restrains, when backward displacement of the engaging part occurs against a force of the biasing device, the backward displacement within a range that the engaging part fails to be disengaged from the spiral guide.